PRODUCTIVE GARDENING 79 



from the plant roots. But that aspect of the 

 subject will claim our attention in another 

 connection. 



How THE PLANT USES WATER AND AIR 



If we would have a clear comprehension of the 

 function of water in a plant, we must go a little 

 more fully into the physiology of plant growth, 

 following the water, with its salts in solution, 

 from the rootlet by which it is absorbed up 

 through the stem of the plant to the leaf. 



In an earlier chapter something has been said 

 as to the forces that operate to make the water 

 rise in seeming defiance of gravitation from the 

 root to the leaf system of a plant of whatever 

 size or height. The rise of the watery juices in a 

 garden plant does not seem, perhaps, quite as 

 mysterious as the rise of the sap in a tall tree. 

 But there is no difference in principle. The laws 

 that govern the movement of the sap are quite 

 the same in each case. 



We saw that there is reason to suppose that 

 the principle of osmosis, acting between the 

 cells, has an important share in transferring 

 water from one cell to another, and ultimately, 

 step by step, from the root to the topmost leaf. 



It should be added, however, that the entire 

 subject of the rise of sap in the tree has been 



